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We report a versatile approach to obtain MoO 3 nanostructures such as nanorods, nanowires, nanobelts, and nanotubes in thin film form on glass substrates, by incorporating ZnO, via RF magnetron sputtering and controlled subsequent oxidation. The nanostructures growth mechanism has been elucidated on the basis of strain field associated with defect-oriented partial screw dislocation induced by ZnO for the drastic variation of the morphology with respect to ZnO incorporating levels from initial tiny nanorods (pure MoO 3 ) to larger nanorods (at 1%), then to aligned and tilted nanowire arrays (at 3 and 5% respectively), afterward to nanobelts (at 7%), and finally to nanotubes (at 10%). Novel properties of ZnO-incorporated MoO 3 nanostructures like enhanced photoluminescence and optical limiting have been brought out. This study opens the door to the potentiality of ZnO-added MoO 3 nanostructures to be used as luminescent transparent conducting materials, saturable absorbers, and optical limiters.

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A novel ZnO incorporated MoO 3 nanostructured thin film system exhibiting high sensitivity and selectivity to ethanol has been developed. The MoO 3 :ZnO nanostructures exhibit enhanced ethanol sensing performance in non-humid and humid (75% r.H. at 21 C) atmospheres compared to the pure MoO 3 layer; with increase in ZnO concentrations, the sensitivity and stability increased, and the response/ recovery time decreased. The response (G ethanol /G air ) of the 25% MoO 3 :ZnO sensor at an operating temperature of 300 C against 500 ppm ethanol is up to 171 under non-humid and 117 under humid (75% r.H.) conditions. By comparing the response of the 25% ZnO added MoO 3 sensor toward various gases (H 2 , CO, C 3 H 6 , CH 4 and C 2 H 5 OH), distinctive selectivity to ethanol is observed. The ethanol sensitivity action over MoO 3 nanostructures can be ascribed to the catalytic oxidation of ethanol to acetaldehyde, and the enhancement of gas sensing response of the MoO 3 :ZnO system can be attributed to more active centers that are obtained from the enhanced oxygen vacancy defects induced by ZnO. The presence of a humid atmosphere has a dramatic influence on the sensor performance towards ethanol; the sensitivity diminishes drastically due to the partial site precluding nature of the adsorbed hydroxyl groups to the analyte. The ZnO incorporated MoO 3 nanostructure based sensing layers in the present work show significantly superior ethanol sensing performance to the works previously reported for various metal oxide systems.

MoO3 nanostructures have been grown in thin film form on five different substrates by RF magnetron sputtering and subsequent annealing; non-aligned nanorods, aligned nanorods, bundled nanowires, vertical nanorods and nanoslabs are formed respectively on the glass, quartz, wafer, alumina and sapphire substrates. The nanostructures formed on these substrates are characterized by AFM, SEM, GIXRD, XPS, micro-Raman, diffuse reflectance and photoluminescence spectroscopy. A detailed growth model for morphology alteration with respect to substrates has been discussed by considering various aspects such as surface roughness, lattice parameters and the thermal expansion coefficient, of both substrates and MoO3. The present study developed a strategy for the choice of substrates to materialize different types MoO3 nanostructures for future thin film applications. The gas sensing tests point towards using these MoO3 nanostructures as principal detection elements in gas sensors.

Abstract. In order to optimize firewood combustion in low-power firewood-fuelled fireplaces, a novel combustion airstream control concept based on the signals of in situ sensors for combustion temperature, residual oxygen concentration and residual un-combusted or partly combusted pyrolysis gas components (CO and HC) has been introduced. A comparison of firing experiments with hand-driven and automated airstream-controlled furnaces of the same type showed that the average CO emissions in the high-temperature phase of the batch combustion can be reduced by about 80 % with the new control concept. Further, the performance of different types of high-temperature CO / HC sensors (mixed-potential and metal oxide types), with reference to simultaneous exhaust gas analysis by a high-temperature FTIR analysis system, was investigated over 20 batch firing experiments ( ∼ 80 h). The distinctive sensing behaviour with respect to the characteristically varying flue gas composition over a batch firing process is discussed. The calculation of the Pearson correlation coefficients reveals that mixed-potential sensor signals correlate more with CO and CH 4 ; however, different metal oxide sensitive layers correlate with different gas species: 1 % Pt / SnO 2 designates the presence of CO and 2 % ZnO / SnO 2 designates the presence of hydrocarbons. In the case of a TGS823 sensor element, there was no specific correlation with one of the flue gas components observed. The stability of the sensor signals was evaluated through repeated exposure to mixtures of CO, N 2 and synthetic air after certain numbers of firing experiments and exhibited diverse long-term signal instabilities.